Mobile construction machines, such as off-highway mining trucks and articulated haul trucks, each include an engine that provides power to associated wheels via a planetary-type transmission (a.k.a., a power-shift transmission). A planetary-type transmission is generally made up of at least three different elements, including a sun gear, a planet carrier having at least one set of planet gears, and a ring gear. The planet gears of the planet carrier mesh with the sun gear and the ring gear. One of the sun gear, planet carrier and ring gear is driven as an input to the transmission, while another of the sun gear, planet carrier, and ring gear rotates as an output of the transmission. The sun gear, planet carrier, planet gears, and ring gear can all rotate simultaneously to transmit power from the input to the output at a first ratio of speed-to-torque and in a forward direction or, alternatively, one of the sun gear, planet carrier, and ring gear can be selectively held stationary or locked to rotate with another gear and thereby transmit power from the input to the output at a second ratio of speed-to-torque and/or in a reverse direction. The change in rotational direction and/or speed-to-torque ratio of the transmission depends upon the number of teeth in the sun and ring gears, the gear(s) that is selected as the input, the gear(s) that is selected as the output, and which gear, if any, is held stationary or rotationally locked with another gear. A hydraulic clutch (also commonly referred to as a brake) is used to hold particular gears stationary and/or to lock the rotation of particular gears together. An exemplary transmission having a planetary gear arrangement and multiple clutches is disclosed in U.S. Pat. No. 8,491,434 of Meyer et al. that issued on Jul. 23, 2013.
Although the conventional power-shift transmission may function adequately in most situations, it can also be slow during clutch engaging. That is, once an operator of a machine selects a particular gear setting to start the machine moving from rest, it may take some time for the corresponding set of clutches to fill with pressurized oil and fully engage. This time, although relatively short, compounds with each excavation cycle during a work shift. The accumulated time spent waiting for the clutches to engage reduces a productivity and efficiency of the machine. In addition, once the clutches engage and the operator depresses an acceleration pedal to start movement of the machine, it may take some time for the associated engine to build up enough power to drive the transmission, especially when the machine is fully loaded. This additional time waiting for the buildup of engine power further reduces productivity and efficiency.
The disclosed drivetrain system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.